I have a mini mac running OSX El Capitan, 10.11.6
Recently it started randomly scrambling some, but not all, of my incoming emails.
I suspected a virus and/or malware. Uninstalled AVG free version (that was interesting!).
Installed Avast free version... Avast claims the machine is clean
Now FireFox is trying to block most of my normal websites, not sure what is going on - FireFox claims:
Your connection is not secure
The owner of www.yahoo.com has configured their website improperly. To protect your information from being stolen, Firefox has not connected to this website.
FireFox did this for the weather service, Geekstogo, Malwarebytes, etc...
I do not see an addon or plugin from Avast so I do not know if it is related.
I saw a post suggesting a scan by Malwarebytes for Mac.
Did that - Malwarebytes claims the machine is clean...
I am still getting random emails scrambled...